The proposed study will determine the effects of lead and PCB (Aroclor 1254) on the immune response of mice to a growing tumor and the effects of contaminant-induced immune alteration on the incidence and growth rate of tumors. Several parameters of immunity will be assessed, including cell-mediated cytotoxicity, serum blocking activity, antibody dependent cell-mediated cytotoxicity, and lymph-kine production. Lead will be administered in the water at levels of 13, 130 or 1300 ppm PB. PCB will be administered in the feed at levels of 10, 100 and 500 ppm. Two tumor systems, the MSV-induced sarcoma and a MCA-induced tumor will be used to compare the differences between a regressive and progressive tumor.